There is a growing need to perform non-contact metrology in processing silicon carbide (SiC) power metal-oxide semiconductor field effect transistors (MOSFETs). For example, the department of defense is currently moving towards platforms and weapons systems that explore electrical powers in innovative ways. To reach the envisioned capabilities in electric propulsion and weapons in a tactical configuration, advances are necessary in the solid state power electronics used to distribute, condition, and regulate the electrical powers.
For instance, the concept of electric warships depends on the ability to rapidly switch power to major loads to meet tactical needs. Current approaches for power distribution being considered for the next generation of carriers and destroyers employ 13.8 kV AC power that is stepped down to 450 V AC by using large (6 ton and 10 m3) 2.7 MVA transformers. The advanced power electronic components of interest under this effort should enable the realization of a solid state power substation (SSPS) that converts the distributed 13.8 kV AC power down to 450 V AC at the same total power level (2.7 MVA) as the current system with a reduction in size of 60% and reduction in weight of approximately 2.6 tons for a single 2.7 MVA transformer. To meet corresponding performance requirements, new wide band-gap semiconductor materials and devices, such as those based on SiC, are required.
Power switching devices and components fabricated from SiC offer a reduction in on-state resistance for high voltage components compared to silicon components. Furthermore, the SiC devices and components offer dramatically lower switching losses, allowing the use of higher frequency AC power; thereby enabling a reduction in the size and weight of passive components in a power conversion circuit. Finally, elevated junction temperature operating capacity up to at least 200 degree centigrade for SiC devices and components allows further reduction of the size of the cooling sub-system.
Under previously funded Department of Defense programs, critical SiC material metrics were demonstrated that have been deemed necessary to enable large area (i.e., 1 cm2), high total power device. In these efforts, small-area devices consistent with the goals of high-voltage switching have been demonstrated in limited quantity. However, these demonstrations have not been consistent with a robust device process and high total power handling capability. Silicon carbide (SiC) MOSFETs, for example, have been demonstrated to exhibit breakdown voltage in excess of 10 kV and specific on-resistance less than 0.15 ohm-cm2. However, issues of achieving high operating currents, stable threshold-voltages and proven reliability of MOS structures remain. Therefore, effort is needed to move beyond single device demonstrations and address manufacturing issues associated with improving the yield, performance, reliability, and cost of future high-power SiC based components. The traditional method used to monitor the quality of a metal-oxide semiconductor (MOS) stack involves at least three mask levels and several days of processing before providing the necessary feedback on the quality and functionality of the device being fabricated. Femtosecond laser induced breakdown spectroscopy (FLIBS) can be used to determine the elemental compositions of a MOSFET surface being fabricated, thereby monitoring the quality of the MOSFET surface. However, FLIBS analysis involves destroying a selected sample surface, such as MOSFET wafer. Capabilities of monitoring interfacial defects without damaging a surface involved, therefore, would advance the current state of the art.